Wu style Taijiquan has a set of strict requirements regarding its practice.
From the external to the internal, each requirement is clearly stated.

The first stage is the practice of external forms starting from the
basics. This stage can be further classified into two phases.

1. The movement of the posture,
and
2. The torso methods (shenfa)

In Taijiquan, it is considered that knowing the movements of the form
indicates the knowledge of the fists, while knowing and understanding the
torso methods is Taiji. With these two combined, then it is called
Taijiquan.

The second stage is the practice of internal structure, also called
the internal energy (neijin), that is the practice of magnificent posture
(qishi). The internal energy appears internally and not externally.
It also indicates the opening and closing of the mind and qi. This
second stage can be further classified into three phases:

1. Separation of the mind and qi;
internally there is a feeling of separation between the muscles and the
bones.
2. Distinguishing between the
mind and qi, that is using the working movements of the separated muscles
and bones, to sense the magnitude of the magnificent posture - big or small,
long or short, thin or thick, etc. Where the mind reaches, the qi
reaches and the energy (jin) reaches. Moving as if not moving; to
have then it exist, not to have then it is non-existence; suddenly appears
and disappears, this must be clearly distinguished in each and every movement,
and finally,
3. the agility in separating the
mind and qi, that is the whole body is united as a whole, where the body
will automatically follow the mind.

Stage 1: External Posture (waixing)

Phase 1: Movements of the posture, from Commencing Form to the Closing
Form there are 96 postures.

1. The hand posture, from the shoulder to the fingers.

Loosening the shoulders: the shoulders must be downwardly loosened.
In every movement the shoulders must be naturally loosen. Avoid lifting
the shoulders.

Dropping of elbows: the elbows must point downwards. When
raising the hand, bend the elbows. When withdrawing the elbows, do
not withdraw the elbows until they are behind the body.

Sitting of the wrist: the wrist must not be flat and bend inwardly.
The Taijiquan form does not contain any hook-hand movements.

Straightening the palm: the palm must be upwardly straightened
and hollow at the center of the palm. Avoid flattening the palm.

The fingers: the five fingers are comfortably stretched open.
Avoid straightening the fingers, the fingertips are slightly pointed upwards.
Both hands must not cross the middle border, each hand protects half the
body.

2. The body posture, in accordance with the principles of starting,
connecting, opening, and closing.

"Starting" - The shoulders align with the hips, that is, forming the
body posture into the four major directions.

"Connecting" - Stepping forward corresponds with raising the hands.
For example, the left leg and the left hand are in front, then the left
hip and the left shoulder must be in front, corresponding with each other,
the body is slightly sideways, that is forming the body posture into the
four sideways (four corners).

"Opening" - similar to the "connecting" formula mentioned above.

"Closing" - The back leg moves to the front, the hand at the back moves
to the front and close (i.e., bring the two hands together), the body turns
from sideways to the front and the shoulders align with the hips, forming
the body posture into four major directions.

3. The footwork, in accordance with the movements
o starting, connecting, opening and closing and transform them into substantiality
and insubstantiality.

"Starting" - Bend the knee and half-squatting down of the substantial
leg, lift the heel and move the insubstantial leg beside the substantial
leg.

"Connecting - Stepping forward of the insubstantial leg. Move
the insubstantial leg forward forty five degrees, the heel lightly landing
on the ground and the sole slightly raised, the knee is slightly bent.

"Opening" - Push forward with the substantial leg, maintain the knee
in a slightly bent position (i.e., d o not straighten the insubstantial
leg), shift the center of gravity forward and form a bow stance with the
insubstantial leg. The landing o the whole insubstantial leg on the
ground to form a bow stance must follow the forward shifting of the center
of gravity. Imagine the knee is directed upwards.

"Closing" - Moving the back leg and place it beside the front leg.
Lift the heel first with the toes touching the ground. When changing
direction, pivot whit the heel of the insubstantial leg, the center of
gravity still remains in the substantial leg.

3. The spirit of the eyes.

When "starting" and "closing," the eyes look forward. When "connecting"
and "closing," look to the left when stepping out with the left leg, likewise
look to the right when stepping out with the right leg. The eyes
must look straight ahead.

4. The head

Keep the head upright. Avoid tilting the head. The neck
must be naturally relaxed. Tucking the chin slightly inwards.

5. The waist

The waist must be straightened. Avoid collapsing or sinking the
waist, and avoid leaning backwards.

6. The hips

The hips must be straightened. Avoid sloping/slanting the hips.
When distinguishing between substantiality and insubstantiality, use the
substantial hip to lift the insubstantial hip.

7. The knees

Avoid downward pressing of the knees. Imagine the knee is always
directed upwards when squatting down, pushing forward or forming a horse
stance.

Phase 2: The essentials of the torso methods

Holding in the chest, stretching the back, keeping the head upright
(suspending the head top), suspending the crotch, loosening the shoulders,
dropping of elbows, wrapping the crotch, and protecting the upper abdomen.

Keeping the body upright, distinguishing between substantiality and
insubstantiality, sinking the qi down to the dantian, attentive spirit
and martial spirit.

The eight torso methods and the five essential requirements are mainly
concerned with the correctness of the internal adjustments. However
for the beginner, the emphasis shall be on the external forms, and slowly
grasp and understand the various aspects of Taijiquan step by step.

The eight torso methods and the five essential requirements cannot be
put into practice all at once. The thirteen principles should be
put into practice only ONE at a time. For example, when practicing
Taijiquan, start with the principle of suspending the crotch, followed
by keeping the head upright. This is to fulfill the requirement of
coordination between the upper and lower parts of the body. Also
this requirement is closely related with keeping the body upright and distinguishing
between substantiality and insubstantiality.

At the next stage, the emphasis should be on holding in the chest and
stretching the back. The key is to practice well the torso method
of holding in the chest is the ability to loosen the shoulders. The
next stage of practice is followed by dropping of elbows, protecting the
upper abdomen and wrapping of crotch. If the eight torso methods
are well practiced, then the ability to sink the qi down to the dantian
can be expressed. All the symmetrical requirements of above and below,
front and rear, left and right, substantiality and insubstantiality, takes
time to practice. After persistent practice, all the principles will
be balanced, coordinated, and integrated. And when these principles
are fully implemented in each and every movement, what is expressed is
Taiji.

In order to coordinate the upper and lower limbs with the trunk of the
body, one should give emphasis on their interrelationships. Also,
to master the skills of Taijiquan, one must pass through the so-called
"storing" stage. "Storing" means to store up or save up, without
causing the external forms and the torso methods to become desultory and
uncoordinated. The key is the integration of the five bows.
In Wu style Taijiquan, the upper and lower limbs and the trunk of the body
are considered as the five bows:

Two bows of the lower limbs with the legs and hips as the tips of the bow,
the knees as the handle of the bow.

Two bows of the upper limbs with the shoulders as the tips of the bow,
the elbows as the handle of the bow.

The bow at the trunk with the lowest vertebra and the lumbar vertebra (where
the shoulders meet the spine as the tips of the bow, the waist as the handle
of the bow.

The word "storing" means the interrelation between the handles of the five
bows. In other words, always concentrate on keeping the elbows down,
imagine the knees are always directed upwards, and combine them with the
torso methods of loosening the shoulders, protecting the upper abdomen,
etc. store the four handles of the above and below at the waist in
order to form the body as a fully stretched bow. This fully stretched
bow then uses the waist as the handle of the bow, the knees and the elbows
as the tips of the bow. Thus the upper and lower limbs, and the trunk
of the body must operate as a unit in order to complete the whole process
of "storing" up of energy.

If the energy (jin) can be stored, it can also be released. This
requirement must be fully understood in the first stage of practice.
hence practitioners must concentrate on this.

Once the "storing" word is fully understood and practiced, then the
movements will have the expression of coordinating between the upper and
lower limbs. At this level, one can then practice the four character
words as starting in the "withdraw-release secret formula" - "holding up,"
"luring," "loosening", and "releasing."

To "store" well requires a good execution of "luring." The "luring"
process must attract a big piece, that is, lure the opponent's to the front,
and store the energy.

If the energy can be stored, it can also be released. One must
release the energy in a straight line. When releasing the energy,
practice the "straight-energy release" first, followed by the practice
of "horizontal energy release," the so-called "one straight-two horizontal."

Stage 2: Internal Posture (neixing)

Stage two involves the practice of internal posture, known as "internal
energy."

Internal posture indicates the internal movement. First it requires
the cultivation of qi in order to have the energy change internally.
This also illustrates the adjustment needed between the mind and qi, which
is the key towards the magnificent postures of Taijiquan.

The first phase is the separation of the mind and the qi, namely the
"opening" character.

Sink the qi downwards, and raise the spirit upwards. The qi follows
the movements of the muscles and sink downwards while the spirit follows
the skeletal system and rises upwards. When practicing Taijiquan,
the feeling of separation between the muscles and the bones must be felt.

Sinking the qi downwards is closing, and so is inhaling.

Raising the spirit upwards is opening, and so is exhaling.

Within opening there is closing, within closing there is opening, within
inhalation there is exhalation; within inhalation there is exhalation;
these are all interdependent. This is in accordance with the practice
guidelines of "The mind and qi server as the primary role, while the muscles
and bones (i.e., body) is secondary," which is the true essence of Taijiquan
practice.

The second phase is distinguishing between the mind and qi, namely
the "clear" character. The magnitude of the magnificent posture -
big or small, long or short, thick or thin, etc. can be adjusted at will,
and accomplish the skill of "action is born of non action" and "suddenly
appears and disappears."

At this level, the "threading" character must be added. That is
all of the body's joints are linked together, with the feeling of "directing
the qi like treading a pearl with nine bends without hindrance."
And in push hands one can express the effect of "where the mind reaches,
the qi reaches and the energy (jin) reaches."

The third and final phase is the agility in separating of the mind and
qi, namely the "agility" character. At this level, one can fully
express the skill of "arousing the spirit of postures," and the "flowing
of qi within the body without hindrance," with the body united as a whole.

According to the ultimate skill of Taijiquan, the expression of whole
body as Taiji is always present regardless of whether practicing the form,
pushing hands, rising, walking, sinking, sleeping, etc.

The above is just a brief introduction to Wu style Taijiquan and its
guidelines for practice.